We may have installed the clutch seal from the crank side instead of the clutch side. common assembly mistake given the GS160 parts manual diagram illustration is incorrect. According to Gene Meredith of Scooters Originali, the GS/SS are the only Vespa motors the clutch seal is installed from the clutch side before the bearing. the GS160 shop manual drawing and directions confirm this assembly sequence.

"If the seal is seated at idle it would run fine. We had to fix 3 GSs from another shop where this seal was put in back wardsâ€¦ im thinking that its under load that the seal pops or spins out. Just running through the issues I have seen on GS/SS. At least you can split a GS case in the engine with just minimal prep work and then you could see behind the crank to check that sealâ€¦"

after going through all of the electrical, electronic and fuel related theories, we have the clutch seal theory and soft seize theory left. We've seen the top half of the cylinder and we know the seal was installed from the crank side. if neither of those theories pan out, I shelve the motor and build another.